1. Field of the Invention:
The invention relates in general to heat exchangers or coolers, and more specifically to cooling fluid-to-air heat exchangers suitable for cooling electrical power apparatus, such as the power transformers used by electrical utilities.
2. Description of the Prior Art:
Over the past decade there has been an increased public awareness that noise is not an inevitable result of of technological society and that it can be annoying. This increased awareness has resulted in enactment of a great variety of local noise control laws. The relatively low noise emissions permitted by these laws are requirements which must be met by the electric utilities.
The noise emissions of electrical power transformers are of considerable concern to utilities because transformers are often located in or near residential areas. The sound of the transformer itself can be attenuated by building sound barriers on one or more sides of the transformer. This method of noise control has been used for many years. The transformer cooling, however, must be located outside of these sound barriers so that there is free air flow through the coolers.
There are a number of different types of coolers than can be supplied with a transformer but for substation transformers only two are in general use. The first of these is made of either wide plate fins or flattened tubes that can provide thermosiphon cooling or pumped oil and/or forced air cooling. These coolers are usually referred to as either radiators or tube coolers.
The second type of cooler usually is made of closely packed finned tubes. The oil is always pumped through the tubes and air is always blown across the tubes. This is commonly called and FOA cooler. This type of cooler has very little thermosiphon capacity.
The primary sources of noise from any cooler are the fans, so the use of thermosiphon cooling seems the correct choice when a low noise level is required. Thermosiphon coolers, however, are very large when compared with an FOA cooler. Further, the heat transfer inside the transformer is not as efficient, and to correct this an increase in the size of the transformer itself is required. Use of thermosiphon coolers where transformers must meet low sound level restrictions is generally ruled against by economic considerations, because land costs are at a premium in such locations and increasing the size of the installation is simply not feasible.
On the other hand, FOA coolers, while requiring much less space and providing more efficient heat transfer inside the transformer coils, generate high noise levels because of the large air flow requirements that must be provided by fans.
Existing FOA transformer oil coolers have sound levels in excess of 70 dBA. Because this type of cooler seems otherwise best suited to locations where this sound level is not permitted, it would be desirable to provide a new and improved FOA cooler with low noise emissions.